95 lines
2.8 KiB
Markdown
95 lines
2.8 KiB
Markdown
Title: Pango Interaction
|
||
|
||
Pango is the text layout system used by GDK and GTK. The functions
|
||
and types in this section are used to obtain clip regions for
|
||
`PangoLayout`s, and to get `PangoContext`s that can be used with
|
||
GDK.
|
||
|
||
## Using Pango in GDK
|
||
|
||
Creating a `PangoLayout` object is the first step in rendering text,
|
||
and requires getting a handle to a `PangoContext`. For GTK programs,
|
||
you’ll usually want to use [method@Gtk.Widget.get_pango_context], or
|
||
[method@Gtk.Widget.create_pango_layout]. Once you have a `PangoLayout`,
|
||
you can set the text and attributes of it with Pango functions like
|
||
[method@Pango.Layout.set_text] and get its size with
|
||
[method@Pango.Layout.get_size].
|
||
|
||
*Note*: Pango uses a fixed point system internally, so converting
|
||
between Pango units and pixels using `PANGO_SCALE` or the `PANGO_PIXELS()`
|
||
macro.
|
||
|
||
Rendering a Pango layout is done most simply with [func@PangoCairo.show_layout];
|
||
you can also draw pieces of the layout with [func@PangoCairo.show_layout_line].
|
||
|
||
### Draw transformed text with Pango and cairo
|
||
|
||
```c
|
||
#define RADIUS 100
|
||
#define N_WORDS 10
|
||
#define FONT "Sans Bold 18"
|
||
|
||
PangoContext *context;
|
||
PangoLayout *layout;
|
||
PangoFontDescription *desc;
|
||
|
||
double radius;
|
||
int width, height;
|
||
int i;
|
||
|
||
// Set up a transformation matrix so that the user space coordinates for
|
||
// where we are drawing are [-RADIUS, RADIUS], [-RADIUS, RADIUS]
|
||
// We first center, then change the scale
|
||
|
||
width = gdk_surface_get_width (surface);
|
||
height = gdk_surface_get_height (surface);
|
||
radius = MIN (width, height) / 2.;
|
||
|
||
cairo_translate (cr,
|
||
radius + (width - 2 * radius) / 2,
|
||
radius + (height - 2 * radius) / 2);
|
||
cairo_scale (cr, radius / RADIUS, radius / RADIUS);
|
||
|
||
// Create a PangoLayout, set the font and text
|
||
context = gdk_pango_context_get_for_display (display);
|
||
layout = pango_layout_new (context);
|
||
pango_layout_set_text (layout, "Text", -1);
|
||
desc = pango_font_description_from_string (FONT);
|
||
pango_layout_set_font_description (layout, desc);
|
||
pango_font_description_free (desc);
|
||
|
||
// Draw the layout N_WORDS times in a circle
|
||
for (i = 0; i < N_WORDS; i++)
|
||
{
|
||
double red, green, blue;
|
||
double angle = 2 * G_PI * i / n_words;
|
||
|
||
cairo_save (cr);
|
||
|
||
// Gradient from red at angle == 60 to blue at angle == 300
|
||
red = (1 + cos (angle - 60)) / 2;
|
||
green = 0;
|
||
blue = 1 - red;
|
||
|
||
cairo_set_source_rgb (cr, red, green, blue);
|
||
cairo_rotate (cr, angle);
|
||
|
||
// Inform Pango to re-layout the text with the new transformation matrix
|
||
pango_cairo_update_layout (cr, layout);
|
||
|
||
pango_layout_get_size (layout, &width, &height);
|
||
|
||
cairo_move_to (cr, - width / 2 / PANGO_SCALE, - DEFAULT_TEXT_RADIUS);
|
||
pango_cairo_show_layout (cr, layout);
|
||
|
||
cairo_restore (cr);
|
||
}
|
||
|
||
g_object_unref (layout);
|
||
g_object_unref (context);
|
||
```
|
||
|
||
The example code above will yield the following result:
|
||
|
||
|